Planet

Node Description and Purpose:
The Planet object is the basis for most scenes in TG2. It is the terrain surface and the atmosphere is created around it. New Planet nodes are initially created with a default Power Fractal Shader v3 surface shader and an Planet Atmospherenode inside their internal node networks.

TG2 can handle zooming into a planet from way out in "space" to very close to the planet surface. However if the scene you're creating is on a kind of local scale rather than planetary scale we recommend that you create the scene around the origin of the planet, which is effectively the North Pole by default. As you move a long way from the origin coordinates begin to lose accuracy and you might start to see things you're not expecting. In many cases this isn't a problem and creating the scene close to the origin works well.

It does however mean that even though TG2 can model whole planets if you want to model a real world location it isn't necessarily a good idea to put that location in the same location as it is in the real world. For example let's say you wanted to model an area in the South Island of New Zealand. If you used the real position on the planet, low down in the Southern Hemisphere, you would likely find problems with coordinate accuracy. It would be much better to reposition the location at the North Pole.

To help with this if you're using georeferenced data you can set the latitude and longitude of the planet origin. This effectively shifts the planet origin to the scene origin where accuracy is better. It's a bit like the whole planet spins round so that the area you're interested ends up at the North Pole.

You can have multiple planets in a scene. For example to create a moon you can make a new Planet object and position and size it appropriately. Here are some sizes of planets etc. in our solar system:

The Moon: 1738000 m

Mercury: 2439000 m

Venus: 6052000 m

Earth (default planet size): 6378000 m

Mars: 3397000 m

Jupiter: 71490000 m

Saturn: 60268000 m

Uranus: 25590000 m

Neptune: 25629000 m

Pluto: 1160000 m

Changing the Size of the Planet
If you want to change the size of the planet then you need to understand how the scene origin and the planet Centre and Radius are related to each other. As described above we typically want the scene origin to be at the North Pole of the planet. Let's say we want a (small!) planet that has a radius of 5000m. If you created a new planet and set its Centre to the scene origin (0, 0, 0) and Radius to 5000 then the North Pole would end up being 5000m away from the origin. See Example A in the image below.

To place the origin at the North Pole we need to offset the position of the planet. It's very easy to do this. Simply set the the Y coordinate of the Centreparameter to the same value as the Radius but make the value negative. Going with our current example we would set the Y coordinate to -5000. Set the X and Z coordinates to 0. This moves the planet "downwards" along the Y axis and aligns the scene origin with the planet surface at the North Pole. Example B in the image below shows what this looks like. You can see how the scene origin is now at the surface of the moved planet.

If you want to change the radius of the default planet then the easiest way to do it is set the Radiusparameter to the new radius. Now copy and paste that value into the Centre Y coordinate and make it negative.

Node Type: Object

Settings:

Show b-box in preview: If this is checked the bounding box of the planet is shown in the 3D Preview.

Render surface: This setting will turn off rendering of the planet surface, leaving only the atmosphere (if that's turned on).

Render atmospher: This setting can turn off rendering of the planet atmosphere.

Lat long at apex: This setting controls the latitude and longitude at the apex or origin of the planet. By default this is set to 0,0 which corresponds to the North Pole on Earth. As mentioned above coordinate accuracy can get worse as you move away from apex. If you are using georeferenced data you can use an appropriate latitude and longitude to remap your area of interest to the origin which will help to avoid accuracy problems.

Centre: This sets the position of the centre of the planet. As this can involve very large distances numbers here are often represented in scientific notation.

Rotation: This sets the rotation of the planet about its centre.

Radius: This sets the radius of the planet. By default it's set to the radius of Earth (6378 km). The radius is set in metres. As this can involve very large numbers values here are often represented in scientific notation.

Import chan file: Click this button to import a chan file to animate the position and rotation of the Planet.

Heading: TBC

Elevation: TBC

Distance: TBC

Surface shader: This sets the shader that creates the planet surface. Typically this will be bottom of the chain of nodes creating the surface layers and terrain of the planet.

Atmosphere shader: This sets the shader which creates the atmosphere of the planet. This will normally be the bottom of the chain of atmosphere and cloud shaders creating the atmosphere for the planet.

Displacement tolerance: TBC

A shader is a program or set of instructions used in 3D computer graphics to determine the final surface properties of an object or image. This can include arbitrarily complex descriptions of light absorption and diffusion, texture mapping, reflection and refraction, shadowing, surface displacement and post-processing effects. In Terragen 2 shaders are used to construct and modify almost every element of a scene.

A single object or device in the node network which generates or modifies data and may accept input data or create output data or both, depending on its function. Nodes usually have their own settings which control the data they create or how they modify data passing through them. Nodes are connected together in a network to perform work in a network-based user interface. In Terragen 2 nodes are connected together to describe a scene.

A parameter is an individual setting in a node parameter view which controls some aspect of the node.

The bounding box is a box which surrounds (or bounds) an object or shader. This box shows the maximum extents of the item inside it. Sometimes abbreviated as "b-box".